1. Field of the Invention
The present invention relates generally to fluid seals used to prevent leakage of fluid from a defined flowpath out of clearance openings formed by parts of a turbomachine. In particular, the invention relates to a non-contacting ejector seal for use in a gas turbine engine.
2. Description of the Known Art
It has been common practice to employ so-called labyrinth seals in turbomachines to reduce leakage of working fluid out of a main flowpath defined by stator and rotor blades of the machine, through clearance openings formed by at least one of the blades, and into an outside region beyond the main flowpath. For example, it is sometimes necessary to extend the rotor blades radially outward beyond the main flowpath to form a discontinuity between the extended rotor blades and points at the outer peripheries of adjacent stator blades. A labyrinth seal is often used to span such a discontinuity to minimize fluid leakage outward from the flowpath. An example of such a seal arrangement is disclosed in U.S. Pat. No. 4,103,899, issued Aug. 1, 1978. Usage of labyrinth seals in other applications in turbomachines is also disclosed in U.S. Pat. Nos. 4,320,903 issued Mar. 23, 1981 and 3,527,053 issued Sept. 8, 1970.
Labyrinth seals have the disadvantage of a finite leakage rate which in some cases may be unacceptable for performance reasons, or because hot flowpath fluids create mechanical problems in the region outside the flowpath, such as high temperature problems or contamination. The leakage rate can be reduced by reduced seal clearance, but there is a minimum seal clearance as a function of seal history and current operating conditions. The minimum seal clearance exists due to out of roundness conditions, differential radial growths, and dynamic loading of the structure. Such mechanical problems may be alleviated in the outside region by buffering the seal with a high pressure fluid. Nonetheless, unacceptable leakage rates exist even with the known fluid buffered labyrinth seal arrangements.